<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button onclick="myFunction()">点我</button>
  <p id="demo"></p>
</body>

<script>
    function myFunction(){
    var carename = "张三";
    document.getElementById("demo").innerHTML = carename;
    }
</script>
</html>